Onset of the north-east monsoon over Tamil Nadu and the rest of the peninsula could be delayed by as much as a week, according to experts.

Normal date of onset is October 20 (Wednesday) but ongoing cyclonic disturbances in the Arabian Sea and the Bay of Bengal are seen fending off monsoon easterlies from establishing over the Southeast Coast.

Sway of westerlies

The south-west monsoon has to withdraw fully to create enabling conditions for the onset of the monsoon in reverse (or north-east monsoon).

The ongoing disturbed weather activity over the Mumbai latitude would only prolong the sway of westerlies over large parts of the peninsula.

The westerlies would have to ultimately yield place for monsoon easterlies. This can take time, and is not expected to happen until the disturbed weather activity migrates to the Chennai latitude.

The spinning up of a fresh ‘low' over East-central Bay of Bengal on Tuesday may have only compounded matters.

A northward track of the system, which is what is indicated by international models, may extend the ongoing rains over Central India.

Onset watch on

According to Dr Y. E A. Raj, Deputy Director-General of Meteorology at the Regional Meteorological Centre, Chennai, told Business Line that he did not see the northeast monsoon setting in at least over the next three days.

The Chennai centre is expected to come out with an announcement over the matter after this, Dr Raj said.

Tamil Nadu and surrounding regions have been witnessing successive normal to above normal northeast monsoon from year 2005.

The law of averages is expected to largely play out this time, too, and near-normal rainfall could be expected as per model predictions.

Meanwhile on Tuesday, India Meteorological Department (IMD) expected the fresh ‘low' over East-central Bay of Bengal on Tuesday to strengthen over the next day or two.

Model indications suggest, however, that a western disturbance dipping in over the Bay of Bengal would scoop up the system and dump it initially over Myanmar-Bangladesh coasts. The same western disturbance with a limb extending into South China Sea would stop the dangerous typhoon Megi, now assessed at Category-3 on the Saffir-Simpson scale of storm intensity, on its track and force it too to take a northward course.

This might put Hong Kong under direct threat from a massive storm intensifying back into Category-4 strength in the basin. Some models see Megi aiming to hit Taiwan.

An IMD update said that fairly widespread rainfall was reported from Konkan, Goa, south Madhya Maharashtra and the Andaman and Nicobar Islands during the 24 hours ending Tuesday morning.

Convective clouds

It was scattered over coastal Andhra Pradesh and north interior Karnataka and isolated over Tamil Nadu and east Madhya Pradesh.

A weather warning said that isolated heavy rainfall would occur over Konkan and Goa on Wednesday.

Forecast valid until Friday said that fairly widespread rain or thundershowers would occur over Mmadhya Maharashtra, Konkan, Goa, cCoastal Karnataka, Kerala and Andaman and Nicobar Islands.

It would be scattered over eEast Uttar Pradesh, Marathwada, Madhya Pradesh, the Northeastern States and North Interior Karnataka.

Extended forecast valid until Sunday said that fairly widespread rainfall would occur over the wWestern Himalayas, the Andaman and Nicobar Islands, eEast Madhya Pradesh, Chhattisgarh, Orissa, North coastal Andhra Pradesh and along the West Coast and the Northeastern States.